Hello and welcome to Case of the Day. I’m Dr Croley and today we’re gonna discuss an interesting case about what we get asked fairly often in the office. We had a young child come in today. She was about 11 or 12 years old and started having trouble seeing at distance. We found out that this person was nearsighted so as soon as we say that then the parents would want to know what does that mean.
A lot of people get confused about nearsightedness, farsightedness and presbyopia and astigmatism and what do all those things really mean. So we’re gonna go over that today. That way you’ll know if you have a particular refractive error then you’ll know what that means and what the terms are.
So we’ll start off with: when we’re born, our eyes are very small. And so in simple terms, a person with a small eye is farsighted or hyperopic and someone with a large eye is nearsighted or myopic, or myopia and for being nearsighted and hyperopia for being farsighted. So, most of us when we’re born and we’re children were farsighted because our eyes are small. As we grow then that changes.
There are two things that determine most of being nearsighted or farsighted, that is, how curved is the cornea – the clear part of your eye in front of the iri – how curved that is and how long and large is your eye. That determines whether you’re nearsighted or farsighted.
So when kids start to grow and get in their early teenage years, that’s commonly when a lot of people or children become nearsighted. They start to notice they can’t see the blackboard at school. Their eyes have grown to the point that they’re now nearsighted. So obviously we put them on glasses or contact lenses and that has to be changed every as often because as they continue to grow, their eye gets bigger and so they get more nearsighted. So people tend to get more nearsighted through their teenage years. Some kids or children may get nearsighted when they’re only six or seven and typically those children are gonna have a very large amount or have a very high myopic correction as they get older because they got nearsighted when they were still young. And so their eyes are gonna grow and they’re gonna get very nearsighted.
And it typically continues and progresses till late teenage years or around twenty or so. That’s the reason why when we consider doing LASIK on someone, that we wait till they’re around age 21 because we want the growing to have stopped and their myopia is not progressing before you do the LASIK because you wanna do this once to correct their vision for the rest of their lives and not do while their eyes are still changing. So a criteria that a lot of eye surgeons use is that you need to be at least 21 and have not gotten more nearsighted more than a half of one diopter in the last two years. So that way we know you’re fairly stable before it’s done.
So we go back to the child who has a small eye and as they grow, they’re hyperopic or have hyperopia and the lens inside of a young person are so pliable and can focus so much that typically in most cases, someone who really has hyperopia or farsightedness, to the point that they really need glasses, is typically they have to have a significant amount of that because kids can focus that out and can still see okay.
What happens sometimes though is because the child is so farsighted that when they try to focus at distance their eyes cross. So when kids get to be 2 or 3 years old, parents start to notice, “My child’s eyes are crossing…,” and that is because as they try to focus and look over the distance, they have to focus the farsightedness out and when we look up close to read our eyes do cross. That part is normal because if you wanna see, both eyes at one point up close they have to cross in. But now they’re having to focus really hard at distance so that crossing occurs and so for those children, we can put them on glasses and relax their eyes from focusing and their cross eyes go away so they can be controlled with glasses.
Another term that people get confused about – hyperopia and farsighted are the same. So someone’s farsighted and hyperopia or hyperopic then that is farsighted. You have to have a plus lens in front of your eye to see clearly. But in general terms, you see better in distance farsighted than you do up close. People who are nearsighted or have myopia see better here up close. They’re nearsighted and do not see well off at a distance.
And then the other thing that happens is when people have astigmatism and people ask, “What’s astigmatism?” Astigmatism in simple terms means that the cornea, the clear part of the front of the eye, is shaped more like a football than a basketball. Sometimes the lens inside the eye can be misshaped a little bit and get a little astigmatism from the lens inside your eye but generally speaking, mostly astigmatism comes from the outside shape of the eye.
So, if we take this tennis ball that’s cut in half then this is round. Then there’s someone who has a round surface does not have astigmatism. If I bend this, now it’s longer this way and shorter this way, like a football. Then when light gets focused through that lens like that or through your cornea, it focuses light to a line, where if it’s round all the light gets focused to a clear point in the back when you don’t have astigmatism.
So then people who have astigmatism notice that maybe the letters start to spread like the ghost images because we’re not focusing to point because of the shape of the eye. And at night they would see a streak around lights at night.
So those are the three common things that we talk about when someone has a refractive error is: that they have myopia, which is nearsightedness; hyperopia and people think that hyperopia means you have no glasses or you see clearly at distance. And it’s not quite true. Hyperopia or farsightedness makes you need a plus lens to see clearly at distance. And then astigmatism has to do with the shape of the eye. The term, the medical term for not really needing any glasses for distance where people typically call that farsightedness is called emmetropia. So actually, emmetrope means you do not need glasses to see at distance. So those are the different eye conditions or refractive errors that we have as far as needing glasses.
So if you have any questions about what we discussed, you can try to contact us through the website and if not, then you have a great day and may God bless you with healthy eyes and great vision.